A 3GPP LTE (3rd Generation. Partnership Project Long Term Evolution; hereinafter, referred to as “LTE”) communication system as an example of a mobile communication system to which the present invention is applicable will be described schematically.
FIG. 1 is a schematic view illustrating the configuration of an E-UMTS network as an example of a mobile communication system.
An E-UMTS (Evolved Universal Mobile Telecommunication System) system is an evolution of the legacy UMTS Universal Mobile Telecommunication System) system. The 3GPP is working on the basic standardization of the E-UMTS system. In general, the E-UMTS system is also called an LTE system.
The E-UMTS network may be largely divided into an E-UTRAN 101 and a CN (Core Network) 102. The E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) 101 includes a UE (User Equipment) 103, eNode Bs or eNBs 104, an AG (Access gateway) 105 which resides at an end of the network in connection to an external network. The AG 105 may be divided into a part for processing user traffic and another part for processing control traffic. In this case, an AG for processing new user traffic may communicate with an AG for processing control traffic via a new interface.
One eNB may manage one or more cells. An interface for transmitting user traffic or control traffic may be established between eNBs. The CN 102 may be comprised of the AG 105, a node for user registration of the UE 103, etc. An interface for distinguishing the E-UTRAN 101 from the CN 102 may be used.
Radio interface protocol layers between a UE and a network may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lowest three layers of the known OSI (Open System Interconnection) reference model in communication systems. Among them, a PHY layer at L1 provides an information transfer service though physical channels and an RRC (Radio Resource Control) layer at L3 controls radio resources between the UE and the network. For this purpose, the RRC layer exchanges RRC messages between the UE and the network. The RRC layer may be distributed across network nodes such as the eNB 104 and the AG 105, or may be confined to the eNB 104 or the AG 105.
The development of wireless communication technology has reached even LTE based on WCDMA. Nonetheless, demands and expectations of users and service providers are on the increase. In addition, considering other wireless access technologies under development, a new technology evolution is needed to have future competitiveness. Per-bit cost reduction, increased service availability, flexible frequency use, a simple structure and an open interface, UEs' appropriate power consumption, etc. are requirements to be fulfilled.
The 3GPP has recently worked on standardization of a successor to LTE. In the specification, the successor to LTE will be referred to as “LTE-Advanced” or “LTE-A”. One of main differences between the LTE system and the LTE-A system is a system bandwidth. The LTE-A system aims to support a broadband of up to 100 MHz. For this purpose, the LTE-A system adopts carrier aggregation or bandwidth aggregation to achieve a broadband using a plurality of component subcarriers.